Heat olive oil in a large saucepan over medium heat.

Add diced celery, carrot, and onion to the saucepan.

Cook the vegetables, stirring occasionally, until softened (about 10 minutes).

Stir in minced garlic and cook until fragrant (about 1 minute).

Season generously with salt and pepper.

Pour in vegetable broth, diced tomatoes (with juices), rinsed lentils, bay leaf, and thyme.

Stir to combine all ingredients.

Cover the saucepan and bring the mixture to a simmer (about 15 minutes).

Reduce heat to low and continue simmering, covered, until lentils and vegetables are tender (about 15 minutes more).

Taste and adjust seasoning with salt or pepper as needed.

Stir in red wine vinegar.

Add spinach and stir until wilted.

For a creamier texture, puree half of the soup in a blender and return it to the pot.